1. Field of the Invention
This invention relates generally to electronic imaging devices and more particularly to a system and method for the automatic capture of salient still images by an electronic imaging device.
2. Description of the Background Art
One of the advantages of digital cameras is their ability to capture images of objects for later manipulation by computer graphics programs. However, digital cameras have a limited dynamic range of exposure sensitivity.
In conventional photography, photographic films capture a wide range of light exposure levels. These films capture detail in both shadow or dark areas and light or bright areas with a single camera exposure of the film. Digital cameras, however, have a much narrower dynamic range due to the use of a charged-coupled device (CCD.) Thus, unlike conventional photographic exposure that captures shadow detail without washing-out image highlights in a high contrast scene, a digital camera will lose a substantial amount of detail in either the darkest areas of the image, or in the brightest areas, or both.
Conventionally, photographers employ a manual method of camera operation known as "bracketing" of exposure setting to record images on photographic film. A photographer takes a first picture at a first exposure setting by adjusting the f-stop on the camera lens and/or the shutter speed dial on the camera body. The photographer then takes a second picture at a second exposure setting for a different light level by changing the f-stop and/or shutter speed. The first exposure setting admits more light for the first picture while the second exposure setting admits less light for the second picture, or vice versa. Thus, the image is said to be "bracketed" between these two settings.
One of the bracketed images on the developed photographic film reveals more detail in the darker areas of the picture while the other bracketed image reveals more detail in the lighter areas. The photographer chooses which of the bracketed images appears best, but conventional photographic methods do not provide any method of combining the images at time of capture to produce the best detail of each. The prior art, however, provides for methods of digitizing the images after the film is developed. Once the bracketed exposures are digitized, a variety of post-production editing programs are available to combine the images.
Automatic cameras allow the photographer to "autobracket" a given image. The photographer sets the range of the bracketing feature (the X factor.) The camera's autobracketing feature then captures a series of images, typically one at the auto metered point, plus one on either side of the metered exposure (usually at +X and -X.) The photographer may then choose which of the images captured by the autobracketing feature to keep, based on the resulting images after processing.
What is required is a method to automatically calculate the need for bracketing, and to calculate the bracketed exposures to capture the image in its full detail. In addition, what is required is a method to put the image data in a form that the computer software may automatically recognize and change into a single, distortion-free image.